Some amateur flushed my system twice, put anti.

Some amateur flushed my system twice, put anti feeze, anti boil in, didnt bleed th system, henxe car heated up, heard a hissing noise when openin bonnet, no water when my son checked, but we found leaking heater tap, replaced it, filled with coolant and water, bled th system, I drove bout 80 k's, temp hot, lifted bonnet, hissing sound, coolant spray on top of radiator, used 2 litres of water, please what is wrong. But twice when gauge up, and ive turned a corner, gauge dropped. Why